Structural Geology L05

Question 1

define faults

Answer 1

any surface or narrow zone with
visible shear displacement

Question 2

What is in fault?

Answer 2

Core and Damage zone

Question 3

explain types of normal fault.

Answer 3

Graben – down-dropped block bounded by
conjugate normal fault

• Horst – relatively uplifted or ‘upthrown’ block
• Half-graben – down-dropped tilted block
  bounded on one side by conjugate fault

Antithetic fault – minor fault, displacement
opposite to main system

• Synthetic fault - minor fault, displacement
  same as main system
• Growth fault – normal slip takes place simultaneously with sedimentation
• Roll-over Anticlines
  – Folding of hanging wall block move down detachment
  – Gravity bends fault lip into antiform
• Listric fault – concave-upward normal fault, dips
  decrease with depth, rotational movement of
  fault blocks
• Detachment fault – low angle (near horizontal)
  normal fault which separate faulted hanging wall
  blocks from unfaulted footwall rocks below

Question 4

Explain types of reverse faults/thrust.

Answer 4

• Thrust sheet (nappe):
  Overthrust hanging wall
  block
• Allocthon: Displaced
  thrust sheet rocks of
  hanging wall
• Autocthon: In place,
  unmoved rock of footwall
• Klippe: Isolated erosional outlier of overthrust strata
• Fenster: Erosional window through thrust sheet
  exposing younger footwall strata
• Ramp-flat geometry: Thrust faults cut up through
  stratigraphy in steps transferring slip from one glide
  horizon to next.
• Horse: Rock developed by overlying roof and
  underlying floor thrust.
• Decollement: Basal shear plane at bottom of thrusted
  sequence

Question 5

Explain geometry of thrust sheet.

Answer 5

• Imbricate fan – fan-like triangular thrust slices which
  converge on single basal thrust.
• Thrust duplex– inclined and stacked thrust horses
  resembling ‘roofing tiles’

Question 6

Relate thrust and bedding layer.

Answer 6

thin-skinned - affect sedimentary only

thick-skinned - affect extent to the basement.

Question 7

Explain strike-slip fault.

Answer 7

• Steeply dipping or vertical faults which accommodate
  horizontal shear within the crust
• Dextral Faults - with right-lateral motion
• Sinistral Faults - with left-lateral motion

Question 8

explain types of strike-slip fault.

Answer 8

• Tear faults – small scale local strike-slip fault
  which are subsidiary to normal and thrust faults
• Transfer fault – larger, regional scale strike-slip
  fault which accommodate slip on normal or
  thrust fault.
  Transform Fault
  – Major strike-slip faults found in association with midocean ridges or plate boundaries
• Transcurrent Fault: Regional scale strike-slip
  faults in continental crust not associated with
  plate boundaries

Question 9

Where did Transfer of slip from one fault segment to another occurs?

Answer 9

• Bend – jog in fault connecting from one segment to
  another
• Step-over – one fault terminates and another begins